Pneumatic radial tire having at least two zigzag belt layers

Abstract

A pneumatic radial tire has at least two belt layers disposed at a tread portion thereof, wherein the two belt layers are constituted by inclining a strip formed by aligning a plurality of reinforcing cords to a tire circumferential direction and extending it zigzag in the tire circumferential direction so that the strip is turned back from the lower belt layer to the upper belt layer at both end portions of the two belt layers, and zone portions in which the reinforcing cords incline to the right in the tire circumferential direction and the zone portions in which the reinforcing cords incline to the left in the tire circumferential direction are alternately arranged.

We claim: 
     
       1. A pneumatic radial tire having at least three belt layers disposed at a tread portion, characterized in that two of said at least three belt layers are constituted by inclining a strip formed by aligning a plurality of reinforcing cords relative to a tire circumferential direction and extending said strip zigzag in the tire circumferential direction in such a fashion that said strip is turned back from the inner belt layer to the outer belt layer at both end portions of said belt layers, zone portion in which said reinforcing cords incline to the left in the tire circumferential direction and zone portions in which said reinforcing cords incline to the left in the tire circumferential direction are alternatively disposed in the tire circumferential direction, and one belt layer having a large number of steel cords arranged at an angle α of inclination of 5 to 65 degrees relative to the tire circumferential direction is disposed inside said two belt layers so that both end portions of said one belt layer are covered by said two belt layers. 
     
     
       2. A pneumatic radial tire according to claim 1, wherein said angle a of inclination satisfies 45°≦α≦65°. 
     
     
       3. A pneumatic radial tire according to claim 2, wherein said angle a of inclination is 54.7°±5°. 
     
     
       4. A pneumatic radial tire according to claim 1, wherein said angle α of inclination satisfies 15°≦α<45°. 
     
     
       5. A pneumatic radial tire according to claim 4, wherein said angle α of inclination is 15° to 40°. 
     
     
       6. A pneumatic radial tire according to claim 1, wherein said reinforcing cords of said two belt layers are organic fiber cords. 
     
     
       7. A pneumatic radial tire according to claim 1, wherein said reinforcing cords of said two belt layers are steel cords. 
     
     
       8. A pneumatic radial tire according to claim 1, wherein the angle θof inclination of said reinforcing cords relative to the tire circumferential direction is 15° to 45°.